In frequency division duplex or FDD radios, transmitter and receiver carrier waves operate simultaneously on different frequencies. FIGS. 1A and 1B illustrate this concept.
FIG. 1A is a block diagram of a pair of FDD radios or an “A, B hop” of an FDD link, in accordance with the prior art. Such radios could be any time of point-to-point or point-to-multipoint radios which may employ FDD for communication signals. As shown, a first radio 102 transmits signals to a second radio 104 using a first frequency range A (the “low”), which frequency range is used by the second radio 104 for receiving signals. In turn, the second radio 104 transmits signals to the first radio 102 using a second frequency range B (the “high”), which frequency range is used by the first radio 102 for receiving signals.
FIG. 1B graphically depicts the transmit (Tx) and receive (Rx) frequency bands A and B for the FDD radios 102 and 104 shown in FIG. 1A.
Because the transmitter and receiver carriers operate on difference frequencies in FDD radios, each terminal in a two radio link (such as that shown in FIG. 1A) is not identical. As such, an FDD radio will typically include a diplexing filter or diplexer at an antenna port to provide isolation between the receiver and transmitter paths and transmitter and receiver selectivity.
FIG. 1C depicts a conventional FDD digital radio configuration. As shown, a modem 110 provides I (in-phase) and Q (quadrature) signals at base band to a mixer 112 in a transmit (Tx) path 130. The mixer 112, which is usually coupled to a local oscillator (not shown) modulates the base band signals to a intermediate frequency or some other frequency approaching or at the transmission carrier frequency for the radio. A set of one or more amplifiers, depicted as amplifiers 114 and 116, boost the signal and provide the amplified signal to a diplexer 118 for transmission via an antenna(e).
The diplexer 118 isolates these transmitted signals from a receive (Rx) path 132, and similarly, isolates signals received by the radio from the Tx path 130 as they are provided to the Rx path 132. The Rx path 132 includes one or more amplifiers (or attenuators) 120 and 124 to amplify the received signal(s). The amplified signal(s) are provided to a mixer 126 for (down) converting into I and Q components at baseband, which are then provided to the modem 110 for further processing.
In the radio configuration shown in FIG. 1C is typically made by a manual connection of the receive and transmit paths to the desired terminals 134 and 136, respectively, of the diplexer 118—depending on whether Tx or Rx should be on the “high” or “low” range of the FDD link for a particular radio (i.e., whether the radio should be configured as an A or B). For example, applying the configuration shown in FIG. 1C to the A, B hop shown in FIG. 1A, assuming terminal 134 is for Tx “low” and terminal 136 is Rx “High”, then if radio 102 of the FDD radio pair shown therein has its Tx path coupled to the terminal 134 and its Rx path coupled to the terminal 136 of the diplexer 118 (and assuming both radios have similar configurations and using the same type of diplexer having the same ports), then the configuration of radio 104 will be reversed such that its Tx path will be coupled to terminal 136 (“high”) and its Rx path will be coupled to terminal 134 (“low”). A pair of radios configured such are typically referred to as a “hop” having “A” and “B” terminals (or radios).
A hop is typically configured by a manufacturer. As such, in a number of applications of hops (e.g., high capacity/speed point-to-point microwave FDD digital radios), end users or customers will typically purchase hop pairings—that is, for every “A” radio, a “B” configured radio will be purchased/used.
Situations may arise, however, in which a user may need an A radio to function as a B radio. For example, a B radio may become non-functional and a spare A radio may be available for swapping. In such situations, typically a manual switching of the diplexer configuration may need to be performed. Unfortunately, manually switching the diplexer configuration may be undesirable since it may be beyond the capabilities of the user and may expose sensitive electronics within a radio's housing to damage.
Another method sometimes used to switch the radio configuration is to place a diversity (or transfer) switch at the terminals of the diplexer, allowing the Tx and Rx paths and the “high” and “low” ports of the diplexer to be reversed. However, such switches generally are mechanical and thus can be relatively expensive, driving up the cost of the radio. Transfer switches may also be relatively difficult to implement because the Tx and Rx paths must be isolated (at the switch) to prevent interference of signals/energy between the Tx and Rx signals at the switch, thus requiring duplication of some of the functionality of the diplexer and additional complexity and cost to reduce the effects of Tx and Rx energy at or near the switch.
Thus, what is needed is an improved system and method for selecting or switching diplexed paths of an FDD radio.